1. Field of the Invention
The present invention relates to an optical unit that includes at least two prisms and facilitates adjustment of an optical axis of incident/reflected light of a reflective display element such as a DMD and a projective display device.
2. Description of the Related Art
In a projective display device, that is, a projector, attention has been paid to a digital micromirror device (DMD) to be a micromirror type video display element as a video display element that can realize an optical unit having a small size and high brightness. The DMD individually controls a swinging angle of a micromirror arranged for each pixel according to video information, separates DMD incident light into a direction (ON light) in which the incident light is made to be incident on a projective lens and a direction (OFF light) in which the incident light is made not to be incident on the projective lens, and performs light modulation corresponding to the video information.
In an optical system of the optical unit using the DMD, it is necessary to make light incident in a state in which an optical axis of the DMD incident light is inclined by a predetermined amount with respect to a surface normal of the DMD, so as to make optical axes of the DMD incident light and the DMD reflected light different from each other. Here, when a rotation angle of a mirror of the DMD is inclined by +θ at the time of ON and is inclined by −θ at the time of OFF, the DMD incident light is generally incident in a state in which the optical axis of the incident light is inclined by 2θ with respect to a center optical axis of the DMD.
As one method of an optical configuration to radiate light to the DMD, a method (hereinafter, referred to as a total reflection prism method) using two triangular prisms of a total reflection prism and a correction prism has been known. In the total reflection prism method, generally, the DMD incident light is made to be incident on the micromirror of the DMD after the DMD incident light is made to transmit the correction prism and the total reflection prism. Meanwhile, the DMD reflected light is totally reflected by a total reflection surface of the total reflection prism and the light is propagated in a projective lens direction, thereby separating a light path of the DMD incident light and a light path of the DMD reflected light. In addition, the correction prism has a function of correcting a light path difference generated by the two prisms by positions of light rays passing through the total reflection prism. Because the total reflection prism method can efficiently separate the DMD incident light and the DMD reflected light, the total reflection prism method becomes a method that is suitable for miniaturization of an optical unit for a projector.
For example, a projector that radiates light source light to the DMD by the total reflection prism is disclosed in JP-2004-240050-A.